Personality development research heavily relies on the comparison of scale means across age. This approach implicitly assumes that the scales are strictly measurement invariant across age. We questioned this assumption by examining whether appropriate personality indicators change over the lifespan. Moreover, we identified which types of items (e.g. dispositions, behaviours, and interests) are particularly prone to age effects. We reanalyzed the German Revised NEO Personality Inventory normative sample ( N = 11,724) and applied a genetic algorithm to select short scales that yield acceptable model fit and reliability across locally weighted samples ranging from 16 to 66 years of age. We then examined how the item selection changes across age points and item types. Emotion–type items seemed to be interchangeable and generally applicable to people of all ages. Specific interests, attitudes, and social effect items—most prevalent within the domains of Extraversion, Agreeableness, and Openness—seemed to be more prone to measurement variations over age. A large proportion of items were systematically discarded by the item–selection procedure, indicating that, independent of age, many items are problematic measures of the underlying traits. The implications for personality assessment and personality development research are discussed. © 2019 European Association of Personality Psychology
